Spriochetes are distinguished from other bacterial phyla by the presence of flagella, sometimes called axial filaments, running lengthwise between the cell membrane and outer membrane. These cause a twisting motion which allows the spirochaete to move about.

The spirochaetes are divided into three families (Brachyspiraceae, Leptospiraceae, and Spirochaetaceae), all placed within a single order (Spirochaetales).

Historical

Salvarsan, the first antibiotic in medical history, was effective against spirochaetes only and was primarily used to cure syphilis.

It has been suggested by biologist Lynn Margulis that eukaryotic flagella were derived from symbiotic spirochaetes, but few biologists accept this, as there is no close structural similarity between the two.